CA2656401C - Paste electrolyte and rechargeable lithium battery containing the same - Google Patents
Paste electrolyte and rechargeable lithium battery containing the same Download PDFInfo
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- CA2656401C CA2656401C CA2656401A CA2656401A CA2656401C CA 2656401 C CA2656401 C CA 2656401C CA 2656401 A CA2656401 A CA 2656401A CA 2656401 A CA2656401 A CA 2656401A CA 2656401 C CA2656401 C CA 2656401C
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- 239000003792 electrolyte Substances 0.000 title claims abstract description 84
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 35
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 34
- 239000002904 solvent Substances 0.000 claims abstract description 19
- 229910003002 lithium salt Inorganic materials 0.000 claims abstract description 12
- 159000000002 lithium salts Chemical class 0.000 claims abstract description 12
- 239000003960 organic solvent Substances 0.000 claims abstract description 9
- 239000004927 clay Substances 0.000 claims description 75
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 24
- 230000008961 swelling Effects 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 8
- 239000011148 porous material Substances 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 7
- 229910052708 sodium Inorganic materials 0.000 claims description 7
- 239000011734 sodium Substances 0.000 claims description 7
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- -1 Li[N(SO2CF2CF3)2] Inorganic materials 0.000 claims description 5
- 239000011248 coating agent Substances 0.000 claims description 5
- 238000000576 coating method Methods 0.000 claims description 5
- 239000011267 electrode slurry Substances 0.000 claims description 5
- 229910000271 hectorite Inorganic materials 0.000 claims description 5
- 150000004649 carbonic acid derivatives Chemical class 0.000 claims description 4
- 150000005676 cyclic carbonates Chemical class 0.000 claims description 4
- 238000001035 drying Methods 0.000 claims description 4
- 230000000149 penetrating effect Effects 0.000 claims description 4
- 125000004122 cyclic group Chemical group 0.000 claims description 3
- GUJOJGAPFQRJSV-UHFFFAOYSA-N dialuminum;dioxosilane;oxygen(2-);hydrate Chemical compound O.[O-2].[O-2].[O-2].[Al+3].[Al+3].O=[Si]=O.O=[Si]=O.O=[Si]=O.O=[Si]=O GUJOJGAPFQRJSV-UHFFFAOYSA-N 0.000 claims description 3
- KWLMIXQRALPRBC-UHFFFAOYSA-L hectorite Chemical compound [Li+].[OH-].[OH-].[Na+].[Mg+2].O1[Si]2([O-])O[Si]1([O-])O[Si]([O-])(O1)O[Si]1([O-])O2 KWLMIXQRALPRBC-UHFFFAOYSA-L 0.000 claims description 3
- 229910052901 montmorillonite Inorganic materials 0.000 claims description 3
- 150000003839 salts Chemical class 0.000 claims description 3
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 claims description 2
- 229910001290 LiPF6 Inorganic materials 0.000 claims description 2
- 238000000498 ball milling Methods 0.000 claims description 2
- 238000002347 injection Methods 0.000 claims description 2
- 239000007924 injection Substances 0.000 claims description 2
- 238000004898 kneading Methods 0.000 claims description 2
- 229910003473 lithium bis(trifluoromethanesulfonyl)imide Inorganic materials 0.000 claims description 2
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 claims description 2
- QSZMZKBZAYQGRS-UHFFFAOYSA-N lithium;bis(trifluoromethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)F QSZMZKBZAYQGRS-UHFFFAOYSA-N 0.000 claims description 2
- 238000004137 mechanical activation Methods 0.000 claims description 2
- 229910052615 phyllosilicate Inorganic materials 0.000 claims description 2
- 229910000166 zirconium phosphate Inorganic materials 0.000 claims description 2
- 238000010296 bead milling Methods 0.000 claims 1
- 125000000129 anionic group Chemical group 0.000 abstract description 10
- 230000001351 cycling effect Effects 0.000 abstract description 6
- 208000020960 lithium transport Diseases 0.000 abstract description 6
- 230000003247 decreasing effect Effects 0.000 abstract description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 10
- 238000003860 storage Methods 0.000 description 10
- 229910001416 lithium ion Inorganic materials 0.000 description 8
- 239000002131 composite material Substances 0.000 description 7
- 238000009792 diffusion process Methods 0.000 description 7
- 239000011244 liquid electrolyte Substances 0.000 description 7
- 238000000034 method Methods 0.000 description 7
- 239000008188 pellet Substances 0.000 description 7
- 239000002002 slurry Substances 0.000 description 7
- 239000002033 PVDF binder Substances 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 229920000642 polymer Polymers 0.000 description 5
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 5
- 239000007787 solid Substances 0.000 description 5
- 239000007784 solid electrolyte Substances 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- 238000007792 addition Methods 0.000 description 4
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 230000002441 reversible effect Effects 0.000 description 4
- 229910032387 LiCoO2 Inorganic materials 0.000 description 3
- 239000006229 carbon black Substances 0.000 description 3
- 229910052681 coesite Inorganic materials 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 239000010416 ion conductor Substances 0.000 description 3
- 239000002931 mesocarbon microbead Substances 0.000 description 3
- 239000004576 sand Substances 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 239000010405 anode material Substances 0.000 description 2
- 238000013459 approach Methods 0.000 description 2
- 239000006182 cathode active material Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000000945 filler Substances 0.000 description 2
- 238000000227 grinding Methods 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- ZRIJXXBGUOBBMX-UHFFFAOYSA-M lithium iodite Chemical compound [Li+].[O-][I]=O ZRIJXXBGUOBBMX-UHFFFAOYSA-M 0.000 description 2
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Chemical compound [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000012528 membrane Substances 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 239000012266 salt solution Substances 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- YEJRWHAVMIAJKC-UHFFFAOYSA-N 4-Butyrolactone Chemical compound O=C1CCCO1 YEJRWHAVMIAJKC-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 206010014415 Electrolyte depletion Diseases 0.000 description 1
- 229910013188 LiBOB Inorganic materials 0.000 description 1
- 229910052493 LiFePO4 Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- 108091081062 Repeated sequence (DNA) Proteins 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 239000006256 anode slurry Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000006257 cathode slurry Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 238000000840 electrochemical analysis Methods 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 239000011256 inorganic filler Substances 0.000 description 1
- 229910003475 inorganic filler Inorganic materials 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- MCVFFRWZNYZUIJ-UHFFFAOYSA-M lithium;trifluoromethanesulfonate Chemical compound [Li+].[O-]S(=O)(=O)C(F)(F)F MCVFFRWZNYZUIJ-UHFFFAOYSA-M 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002114 nanocomposite Substances 0.000 description 1
- 239000005486 organic electrolyte Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000009790 rate-determining step (RDS) Methods 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- ADZWSOLPGZMUMY-UHFFFAOYSA-M silver bromide Chemical compound [Ag]Br ADZWSOLPGZMUMY-UHFFFAOYSA-M 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000002522 swelling effect Effects 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0085—Immobilising or gelification of electrolyte
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Primary Cells (AREA)
Abstract
The present invention provides a paste electrolyte comprising an organic solvent of not high dielectric constant, soluble lithium salts, and clays, with the clays being swollen by the solvent, and rechargeable lithium batteries containing the paste electrolyte. The paste electrolyte according to the present invention can improve the electrochemical properties and cycling stability of rechargeable lithium batteries by limiting the anionic transport between anode and cathode without significantly decreasing the lithium transport rate, particularly during fast charge and discharge.
Description
Description PASTE ELECTROLYTE AND RECHARGEABLE LITHIUM
BATTERY CONTAINING THE SAME
Technical Field [1] The present invention relates to a paste electrolyte comprising an organic solvent of not high dielectric constant, soluble lithium salts, and clays, with the clays being swollen by the solvent, and rechargeable lithium batteries containing the paste electrolyte which separates anode and cathode to allow fast diffusion of lithium ions but hinders a fast anionic diffusion.
Background Art [21 Liquid electrolyte is applied in most commercial rechargeable lithium batteries. Al-ternatively, a so-called gel polymer, i.e. polymer with a very large fraction of liquid electrolyte is applied. These electrolytes have relatively high ionic conductivity, whereas the Li transference number thereof is typically below 0.5, i.e., t Li+
< 0.5. As a result, anionic diffusion dominates during fast charge and discharge.
[31 This low Li transference number causes dramatic and undesired effects.
More specifically, during fast charge or discharge, anions counter-diffuse and a gradient of salt concentration is established in the electrolyte, whereby the electrolyte kinetically depletes. Consequently, the electrolyte conductivity decreases to cause poor rate performance. Furthermore, the electronic potential of lithium plating is altered, and particularly during fast charge in a region near to the anode, the electrolyte may exceed the electronic stability window, causing accelerated reductive electrolyte de-composition.
[41 As a result, it is strongly desired to slow down the anionic diffusion. In an ideal case, a Li-ion conductive membrane with the Li transference number, t Li+ =1, separates the electrolyte-soaked anode and cathode; however, no practical ways that are able to achieve it have been found yet. Generally, the charge transfer of lithium at the solid electrolyte - liquid electrolyte interface of such membranes is too slow.
[51 Numerous patents suggest composites of polymer (e.g., PEO) with inorganic fillers (e.g., nano-Al z O z or silica) to create solid electrolytes with improved conductivity and an increased Li-transference number. However, in spite of the significant progress, the achieved transport properties are far away from real commercial requirements.
It is doubtful if further progress can be achieved. The improvement in these composites is attributed to structural changes (less crystallinity) of the polymer near to the filler particle, and thus, further significant improvements are not likely.
[61 Another approach is known in the area of solid electrolytes. Here metal-halogenite
BATTERY CONTAINING THE SAME
Technical Field [1] The present invention relates to a paste electrolyte comprising an organic solvent of not high dielectric constant, soluble lithium salts, and clays, with the clays being swollen by the solvent, and rechargeable lithium batteries containing the paste electrolyte which separates anode and cathode to allow fast diffusion of lithium ions but hinders a fast anionic diffusion.
Background Art [21 Liquid electrolyte is applied in most commercial rechargeable lithium batteries. Al-ternatively, a so-called gel polymer, i.e. polymer with a very large fraction of liquid electrolyte is applied. These electrolytes have relatively high ionic conductivity, whereas the Li transference number thereof is typically below 0.5, i.e., t Li+
< 0.5. As a result, anionic diffusion dominates during fast charge and discharge.
[31 This low Li transference number causes dramatic and undesired effects.
More specifically, during fast charge or discharge, anions counter-diffuse and a gradient of salt concentration is established in the electrolyte, whereby the electrolyte kinetically depletes. Consequently, the electrolyte conductivity decreases to cause poor rate performance. Furthermore, the electronic potential of lithium plating is altered, and particularly during fast charge in a region near to the anode, the electrolyte may exceed the electronic stability window, causing accelerated reductive electrolyte de-composition.
[41 As a result, it is strongly desired to slow down the anionic diffusion. In an ideal case, a Li-ion conductive membrane with the Li transference number, t Li+ =1, separates the electrolyte-soaked anode and cathode; however, no practical ways that are able to achieve it have been found yet. Generally, the charge transfer of lithium at the solid electrolyte - liquid electrolyte interface of such membranes is too slow.
[51 Numerous patents suggest composites of polymer (e.g., PEO) with inorganic fillers (e.g., nano-Al z O z or silica) to create solid electrolytes with improved conductivity and an increased Li-transference number. However, in spite of the significant progress, the achieved transport properties are far away from real commercial requirements.
It is doubtful if further progress can be achieved. The improvement in these composites is attributed to structural changes (less crystallinity) of the polymer near to the filler particle, and thus, further significant improvements are not likely.
[61 Another approach is known in the area of solid electrolytes. Here metal-halogenite
2 solid electrolyte ionic conductors like lithium iodite (LiI) or silver halogenides (AgCI, AgBr, AgI) tc.) are "heterogeneously doped" using submicrometer particles (e.g., Al z O
3). In this approach, the transport properties can be improved because the grain boundary conduction exceeds the bulk conduction. The increase of grain boundary conductivity is explained by the concept of space charge. This concept has in detail been summarized in "Ionic conduction in space charge regions" Q. Maier, Prog.
Solid State Chem, 23, 171).
[7] A similar concept has been applied to liquid electrolytes. "Heterogeneous doping" of liquid electrolytes has been described in "Second phase effects on the conductivity of non-aqueous salt solutions: soggy sand electrolytes" (A. J. Bhattacharya and J
Mair, Advanced Materials 2004. 16. 811) and "Improved Li-battery Electrolytes by heterogeneous Doping of Nonaqueous Li-salt solution" (A. J. Bhattacharya. Mockael Dolle and J Mair, Electroch. Sol.
State Letters 7 (11) A432) In these cases, addition of fine particles such as Al20_, Ti02, SiO2, etc. to the electrolyte results in "soggy sand electrolytes". Soggy sand means that rigid solid particles (which may have small sizes) coexist with a liquid phase. Among them, in the case of Si02, an improvement of transport properties is achieved: however, it is not recommended to apply SiO2 because in real batteries it causes undesired side reactions consuming lithium, which has been investigated and described in detail in chapter 6 of Zhaohui Chen"s PhD
thesis (Improved Positive Electrode Materials for Li-Ion Batteries: Exploring the High Specific Capacity of LiCoO2 and High Rate Capability of LiFePO4, Dalhousie university, Halifax. 2003).
[8] Therefore, there is strong need for liquid electrolyte being able to allow the fast diffusion of lithium ions but that hinders a fast anionic diffusion.
Disclosure of Invention Technical Problem [9] The objects of the present invention are to completely solve the problems described above.
[10] An object of the present invention is to provide a paste electrolyte being able to improve the electrochemical properties and cycling stability of rechargeable lithium batteries by limiting the anionic transport between anode and cathode without sig-nificantly decreasing the lithium transport rate, particularly during fast charge and discharge.
[11] Another object of the present invention is to provide a rechargeable lithium battery containing the above paste electrolyte.
Technical Solution [12] In order to accomplish these objects, there is provided in the present disclosure a paste electrolyte comprising an organic solvent of not high dielectric constant, soluble lithium salts, and clays, with the clays being swollen by the solvent.
Solid State Chem, 23, 171).
[7] A similar concept has been applied to liquid electrolytes. "Heterogeneous doping" of liquid electrolytes has been described in "Second phase effects on the conductivity of non-aqueous salt solutions: soggy sand electrolytes" (A. J. Bhattacharya and J
Mair, Advanced Materials 2004. 16. 811) and "Improved Li-battery Electrolytes by heterogeneous Doping of Nonaqueous Li-salt solution" (A. J. Bhattacharya. Mockael Dolle and J Mair, Electroch. Sol.
State Letters 7 (11) A432) In these cases, addition of fine particles such as Al20_, Ti02, SiO2, etc. to the electrolyte results in "soggy sand electrolytes". Soggy sand means that rigid solid particles (which may have small sizes) coexist with a liquid phase. Among them, in the case of Si02, an improvement of transport properties is achieved: however, it is not recommended to apply SiO2 because in real batteries it causes undesired side reactions consuming lithium, which has been investigated and described in detail in chapter 6 of Zhaohui Chen"s PhD
thesis (Improved Positive Electrode Materials for Li-Ion Batteries: Exploring the High Specific Capacity of LiCoO2 and High Rate Capability of LiFePO4, Dalhousie university, Halifax. 2003).
[8] Therefore, there is strong need for liquid electrolyte being able to allow the fast diffusion of lithium ions but that hinders a fast anionic diffusion.
Disclosure of Invention Technical Problem [9] The objects of the present invention are to completely solve the problems described above.
[10] An object of the present invention is to provide a paste electrolyte being able to improve the electrochemical properties and cycling stability of rechargeable lithium batteries by limiting the anionic transport between anode and cathode without sig-nificantly decreasing the lithium transport rate, particularly during fast charge and discharge.
[11] Another object of the present invention is to provide a rechargeable lithium battery containing the above paste electrolyte.
Technical Solution [12] In order to accomplish these objects, there is provided in the present disclosure a paste electrolyte comprising an organic solvent of not high dielectric constant, soluble lithium salts, and clays, with the clays being swollen by the solvent.
4 PCT/KR2006/002675 [13] Therefore, the paste electrolyte in accordance with the present invention is a mixture of a specific organic solvent, soluble lithium salts and specific clays, in other words, a liquid composite of liquid organic electrolyte with swollen clay.
[14] The paste electrolyte of the present invention limits the anionic transport between anode and cathode to improve the electrochemical properties of rechargeable lithium batteries, particularly fast charge/discharge properties, without significantly decreasing the lithium transport rate, and also guarantees long term chemical stability in contact with lithium salts to increase the cycling stability of rechargeable lithium batteries. On the other hand, the paste electrolyte of the present invention does not decrease the energy density of rechargeable lithium batteries and does not increase the price thereof unreasonably.
[15] The organic solvent in the paste electrolyte of the present invention has a low to medium dielectric constant (e), desirably, 3 < e < 50. A lower dielectric constant un-desirably prevents the clay from swelling in the electrolyte. On the other hand, where the dielectric constant is larger than the preferred region, the anionic transport in the electrolyte is then not sufficiently hindered. In a preferred embodiment, the solvent contains more than 50% by volume, more preferably more than 60% by volume of one or more linear carbonates such as ethyl methyl carbonate, and less than 50% by volume, more preferably less than 40% by volume of one or more cyclic carbonates such as ethylene carbonate or cyclic esters such as gamma-BL.
[16] The soluble lithium salts dissolved in the solvent include, for example, but are not limited to LiPF6, LiBF4, Li-Beti (Li[N(SO2CF2CF3)2], LiBOB (lithium Bis(oxalato)borate), lithium trifluoromethanesulfonate, lithium Bis(trifluoromethanesulfonyl)imide etc. in a total concentration exceeding 0.5 mol /
liter solvent. The volume fraction of the liquid electrolyte (i.e.
solvent+salt) in the paste electrolyte is more than 75% but less than 99%.
[17] The clays used in the present invention include, for example, but are not limited to hectorite, montmorillonite, alpha-zirconium phosphate, etc., and preferably they contain lithium and/or sodium. The clays may be used in any combination of two or more. The content of clays in the paste electrolyte is in the range of 1 - 25 % by weight based upon the total weight of the paste electrolyte. In the paste electrolyte, the clays are exfoliated by the organic solvent. The general size of exfoliated clay sheets does not exceed 2 micrometers, more preferably is significantly less than 0.5 mi-crometers.
[18] Generally, different clays have different properties. Usually they easily swell in water, but the swelling is more difficult to occur in organic solvent.
According to the present invention, clays with high swelling ability are more preferable. One example for the clays with very good swelling properties is synthetic phyllosilicate containing sodium. In some cases, sodium is undesired; therefore, in the prior art, clays have been sometimes treated to ion exchange sodium for lithium. Lithium-containing clays, however, have less swelling ability. Inventors of the present invention discovered that this ion exchange is not required. The small content of sodium is beneficial to the cycling stability of lithium cells or at least does not harm it.
[191 Some prior arts disclose use of clay in electrolyte or electrode for rechargeable lithium batteries but none of them teach or suggest the paste electrolyte in accordance with the present invention. To help the understanding to the present invention, these prior arts are illustrated in below.
[201 US 2004/0126667A1 discloses an ion conducting nano-composite comprising a polymer such as PEO and negatively charged synthetic clays such as Si-rich hectorite.
This composite is a polymer-clay composite different from the paste electrolyte of the present invention, and as mentioned already in the above, the achieved transport property is far away from real commercial requirements and also it is unlikely to expect a further improvement.
[211 JP 96-181324 discloses a solid electrolyte being a lithium conductive clay such as montmorillonite containing a water soluble lithium salt such as Li2SO4, which is also different from the paste electrolyte of the present invention, likewise in comparison with US 2004/0126667A1 as above.
[221 US 6,544,689 B 1 discloses a composite electrolyte consisting of a dielectric solution with high dielectric constant (50 - 85) and a clay filler such as Li-hectorite, dispersed into it. Since this patent applies the Li-hectorite/solution composite as a solid Li-ion conductor, the preferable dielectric solution is free of dissolved lithium salts. On the other hand, the paste electrolyte of the present invention does not comprise dielectric solutions free of dissolved lithium salts and also does not intended to facilitate a solid Li-ion conductor. It should be noted that the present invention focuses on an enhancement of the transport properties in the liquid phase. Desired interactions between the salt ions and the clay surface occur within a small region called "space charge region". A desired interaction is, for example, an interaction between an acidic clay surface and the salt anion, which enhances the lithium transport number and lithium ionic conductivity. In the case of high dielectric solvents, the space charge region is small and thus an excessive volume fraction of clay is required. The paste electrolyte of the present invention comprises a solvent with low to medium dielectric constant, exceeding those of pure linear carbonates (in the case of ethyl-methyl-carbonate (EMC), E _ 3) but being significantly less (E < 50) than those of pure cyclic carbonates (in the case of ethylene carbonate (PC), E - 65).
[231 JP H09-115505 discloses electrodes comprising a lithium transition metal in which powderous particles are coated with sintered clay. This technique is absolutely different from the present invention in view of kinds of application and materials.
[24] The present invention also provides a rechargeable lithium battery containing the paste electrolyte as defined above between anode and cathode.
[25] The paste electrolyte may be in a form of layer. A layer of the paste electrolyte (hereinafter, sometimes referred to as "paste electrolyte layer") can be located in any inner place of lithium battery so long as the paste electrolyte layer can separate anode and cathode to limit the anionic transport between the anode and cathode without sig-nificantly decreasing the lithium transport rate. Such separation may be achieved by one or more of the following:
[26] the paste electrolyte is embedded in the pores of the cathode;
[27] the paste electrolyte is applied as a thin layer between the cathode and separator, eventually penetrating the separator;
[28] the paste electrolyte is embedded in the pores of separator;
[29] the paste electrolyte is applied as a thin layer between the anode and separator, eventually penetrating the separator; and [30] the paste electrolyte is embedded in the pores of the anode.
[311 The layers of clay can be achieved by many different methods. In principle, it is possible to deposit (for example, by coating) a layer of paste-type electrolyte-swollen clay during an assembly of a battery cell. This method, however, is not easy to implement at the production level.
[32] In an embodiment according to the present invention, it is possible to deposit a layer of clay, swollen by a suitable solvent such as water, ethanol, NMP and the like, followed by drying. This method is especially suitable to coat a layer of clay onto the separators or onto electrodes. After assembly of a battery, electrolyte is injected and the dried layer slowly swells with electrolyte and forms the desired paste electrolyte layer.
[33] Another preferred method is to add the clay swollen by a suitable solvent to an electrode slurry before coating of the electrode slurry into electrodes. As an example, clay swollen by N-methyl-2-pyrrolidone (NMP) can be added to the NMP+PVDF-based electrode slurry containing the electrochemical active cathode or anode material.
Alternatively, the clay swollen by water can be added to a water-based slurry.
After coating and drying, the clay is located within the pores of the electrode, and after battery assembly and electrolyte injection, this clay is swollen by the electrolyte.
[34] The swelling of clay by a solvent such as water, ethanol and NMP may be supported by mechanical activation including, for example, but is not limited to ballmilling, beadniilling or kneading a mixture of clay and solvent.
[35] The other constitutional elements for rechargeable lithium batteries and the processes for preparation thereof are well known in the art to which the present invention pertains, thus the detailed description about them is omitted in the present disclosure.
Brief Description of the Drawings [36] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
[37] FIG. 1 is a graph showing the results of electrochemical test (cycle 1 and discharge rate performance) of the coin cells containing thick-electrode pellets in Example 5.
Mode for the Invention [38] Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for the purpose of illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention.
[39]
[40] [Example 1] Swelling of clay in electrolyte [41] A commercial synthetic clay ("optigel SH", SuedChemie, Germany) was used.
The clay was in the form of a coarse, free flowing powder. The clay was dried at 180C to lower the water content. 10 g of the dried clay was added to 20 g of electrolyte (1M
LiPF 6 in EC/EMC (1 : 2)). After several weeks of storage at room temperature in a sealed PP vial in a glovebox, a homogeneous white paste was achieved. No mechanical force like grinding, agitating etc. was applied. This experiment demonstrates that the used clay swells in an electrolyte with medium dielectric constant.
[42]
[43] [Example 2] Swelling of clay in NMP
[44] A mixture of 86% NMP and 14%(w/w) clay was ballmilled using a planetary mill.
A semi-transparent, homogeneous white paste was achieved.
[45]
[46] [Example 3] Addition of clay paste to electrode slurries [47] The clay-NMP paste of Example 2 was added to an NMP-based anode (MCMB) and an NMP-based cathode (Li-manganese-spinel) slurry, respectively, followed by homogenizing. The total content of clay per active materials in the slurry was 1%
(w/w). The compositions (active material: PVDF: carbon black) of the cathode and anode slurry were 94: 3 : 3 and 94.5 : 4.5 : 1, respectively.
[48] The slurries were coated on aluminum foil and copper foil, respectively, and then dried. An improved adhesion was observed, compared with electrodes coated from the slurry without clay.
[49]
[50] [Example 4] Storage properties of clay containing ion cells [51] Coin-full cells were prepared using the electrodes of Example 3. The total 4 types of cells were prepared as the following:
[52] (i) anode with clay - cathode with clay [53] (ii) anode with clay - cathode without clay [54] (iii) anode without clay - cathode with clay [55] (iv) anode without clay - cathode without clay.
[56] Storage properties of charged cells (65 C) and cycling stability (50 C) were in-vestigated. Cells containing clay in the anode showed clearly improved storage properties.
[57] 2 cells of each type were tested. First cells were tested for the purpose of measuring rate performance & capacity. The rate performance was similar for all cells.
Then cells were charged to 4.2 V and stored for 3 days at 65 C. After storage, cells were cycled at room temperature for 2 cycles (3.0 - 4.2 V) starting with discharge to 3.0 V.
While the first discharge capacity is the remaining capacity, the 2nd discharge capacity is the reversible capacity. After this test, another storage was performed at 65 C
for 10 days.
The results for the cell showing two with better results are summarized in below.
[58] <TABLE 1>
[59]
Before storage After storage 1 After storage 2 Cathode fully charged fully charged capacity for 3d 65"C for 10d 65''C
(mAh/g) remaining reversible remaining reversible Anode & cathode 91.6 70.0 77.0 49.2 56.7 with clay (100%) 76.4% 84.0% 53.7% 61.9%
Anode clay 93.0 72.8 78.1 49.4 56.6 Cathode no clay (100%) 78.2% 83.9% 53.1% 60.8%
Anode no clay 90.0 63.1 69.5 22.2 31.03 Cathode clay (100%) 70.1% 77.2% 24.6% 34.5%
Anode & cathode 90.8 66.6 72.1 40.2 47.0 without clay (100%) 73.4% 79.4% 44.2% 51.8%
[60] The above result shows that the addition of clay has a positive effect on the storage properties (remaining and reversible capacity) of Li-batteries.
[61]
[62] [Example 5] Change of electrolyte properties [63] It is difficult to exactly measure transport properties of electrolyte, i.e., conduction and transference number. Therefore, in this experiment, the ionic transport of electrolyte was indirectly measured by comparing the rate performance of cells with clay with those of cells without clay. In this connection, it is important to achieve a similar cell geometry such as thickness of electrodes, porosity, loading, etc., and it is also important that the electrolyte transport is the only rate-limiting step.
To achieve those requirements coin cells with pellet type electrodes were prepared.
[64] The active anode material was MCMB and the active cathode material was LiCoO2 . The cathode mass was 239 - 240.2 mg. The composition (LiCoO2 : PVDF : Carbon Black : Clay) was 85 : 7 : 8 for cathodes without clay and 85 : 6.07: 6.93: 2 and 85 : 4 : 4 :7 for cathodes with clay, respectively. The thickness of pellets was 0.48 - 0.51 mm and the diameter was 15 mm. The anode pellets were free of clay and had a composition (MCMB : PVDF : Carbon Black) of 90 : 7: 3. The anode mass was 149.9 150.4 mg. The thickness of the pellets was 0.49 - 0.52 mm. The diameter was 16 mm. Electrode pellets were prepared by drying an NMP-PVDF-based slurry, followed by grinding and controlled pressing of pellets. Clay-containing slurries were prepared by adding the clay-NMP paste of Example 2.
[65] Coin cells were assembled. After very slow formation (C/100, 1C=150 mA/g cathode) for 10h, the cells were charged to 4.25 V. The charging occurred by repeated sequences of C/20 charge for 2 h (or until 4.25 V cutoff was reached) and rest for 2 h. All electrochemical testing was performed at 25 C.
[66] Discharge was at C/20, C/10 and C/5 rate. The results of the best 3 cells out of 9 prepared cells are expressed in FIG 1. First, it is important to note that cells with a total thickness of 1mm are only limited by the electrolyte transport. All other processes such as electronic conduction, solid diffusion within single particles and the like are orders of magnitude slower. The cell with 7% clay clearly shows the largest electrolyte resistance, which can be seen by the gap between 1st charge and 1st discharge curve, as well as by the larger relaxation during the rest periods during the charge. We also see the larger electrolyte resistance of the 7% clay cell during discharge. The gap between C/20 and C/5 discharge curve is clearly larger for 7% clay compared with 0 or 2%
clay. Additionally the discharge capacity at a slow rate is less, and the reason for this is not clear. However, despite the larger electrolyte resistance and the lower capacity, the 7% clay cell shows a good C/5 discharge capacity. This result strongly illustrates that the Li transference number of the electrolyte in the 7% clay cell increases.
As a result, there is less electrolyte depletion, and the discharge profile bends more slowly down.
The results are summarized in TABLE 2 below.
[67] <TABLE 2>
[68]
Discharge capacity Discharge capacity Discharge capacity (C/20) mAh/g (C/1C) mAh/g (C/5) mAh/g Clay: 0% 144 (100%) 120 (83%) 91 (63%) Clay 2% 143(100%) 127 (89%) 97(68%) Clay 7% 131 (100%) 122 (93%) 96(73%) [69] As can be seen in TABLE 2, the discharge capacities associated with the discharge at C/20 clearly increase with the increasing content of clay.
Industrial Applicability [70] As apparent from the foregoing, the paste electrolyte according to the present invention can improve the electrochemical properties and cycling stability of rechargeable lithium batteries by limiting the anionic transport between anode and cathode without significantly decreasing the lithium transport rate, particularly during fast charge and discharge.
[71] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modi-fications, additions and substitutions are possible, without departing from the scope of the invention as disclosed in the accompanying claims.
[14] The paste electrolyte of the present invention limits the anionic transport between anode and cathode to improve the electrochemical properties of rechargeable lithium batteries, particularly fast charge/discharge properties, without significantly decreasing the lithium transport rate, and also guarantees long term chemical stability in contact with lithium salts to increase the cycling stability of rechargeable lithium batteries. On the other hand, the paste electrolyte of the present invention does not decrease the energy density of rechargeable lithium batteries and does not increase the price thereof unreasonably.
[15] The organic solvent in the paste electrolyte of the present invention has a low to medium dielectric constant (e), desirably, 3 < e < 50. A lower dielectric constant un-desirably prevents the clay from swelling in the electrolyte. On the other hand, where the dielectric constant is larger than the preferred region, the anionic transport in the electrolyte is then not sufficiently hindered. In a preferred embodiment, the solvent contains more than 50% by volume, more preferably more than 60% by volume of one or more linear carbonates such as ethyl methyl carbonate, and less than 50% by volume, more preferably less than 40% by volume of one or more cyclic carbonates such as ethylene carbonate or cyclic esters such as gamma-BL.
[16] The soluble lithium salts dissolved in the solvent include, for example, but are not limited to LiPF6, LiBF4, Li-Beti (Li[N(SO2CF2CF3)2], LiBOB (lithium Bis(oxalato)borate), lithium trifluoromethanesulfonate, lithium Bis(trifluoromethanesulfonyl)imide etc. in a total concentration exceeding 0.5 mol /
liter solvent. The volume fraction of the liquid electrolyte (i.e.
solvent+salt) in the paste electrolyte is more than 75% but less than 99%.
[17] The clays used in the present invention include, for example, but are not limited to hectorite, montmorillonite, alpha-zirconium phosphate, etc., and preferably they contain lithium and/or sodium. The clays may be used in any combination of two or more. The content of clays in the paste electrolyte is in the range of 1 - 25 % by weight based upon the total weight of the paste electrolyte. In the paste electrolyte, the clays are exfoliated by the organic solvent. The general size of exfoliated clay sheets does not exceed 2 micrometers, more preferably is significantly less than 0.5 mi-crometers.
[18] Generally, different clays have different properties. Usually they easily swell in water, but the swelling is more difficult to occur in organic solvent.
According to the present invention, clays with high swelling ability are more preferable. One example for the clays with very good swelling properties is synthetic phyllosilicate containing sodium. In some cases, sodium is undesired; therefore, in the prior art, clays have been sometimes treated to ion exchange sodium for lithium. Lithium-containing clays, however, have less swelling ability. Inventors of the present invention discovered that this ion exchange is not required. The small content of sodium is beneficial to the cycling stability of lithium cells or at least does not harm it.
[191 Some prior arts disclose use of clay in electrolyte or electrode for rechargeable lithium batteries but none of them teach or suggest the paste electrolyte in accordance with the present invention. To help the understanding to the present invention, these prior arts are illustrated in below.
[201 US 2004/0126667A1 discloses an ion conducting nano-composite comprising a polymer such as PEO and negatively charged synthetic clays such as Si-rich hectorite.
This composite is a polymer-clay composite different from the paste electrolyte of the present invention, and as mentioned already in the above, the achieved transport property is far away from real commercial requirements and also it is unlikely to expect a further improvement.
[211 JP 96-181324 discloses a solid electrolyte being a lithium conductive clay such as montmorillonite containing a water soluble lithium salt such as Li2SO4, which is also different from the paste electrolyte of the present invention, likewise in comparison with US 2004/0126667A1 as above.
[221 US 6,544,689 B 1 discloses a composite electrolyte consisting of a dielectric solution with high dielectric constant (50 - 85) and a clay filler such as Li-hectorite, dispersed into it. Since this patent applies the Li-hectorite/solution composite as a solid Li-ion conductor, the preferable dielectric solution is free of dissolved lithium salts. On the other hand, the paste electrolyte of the present invention does not comprise dielectric solutions free of dissolved lithium salts and also does not intended to facilitate a solid Li-ion conductor. It should be noted that the present invention focuses on an enhancement of the transport properties in the liquid phase. Desired interactions between the salt ions and the clay surface occur within a small region called "space charge region". A desired interaction is, for example, an interaction between an acidic clay surface and the salt anion, which enhances the lithium transport number and lithium ionic conductivity. In the case of high dielectric solvents, the space charge region is small and thus an excessive volume fraction of clay is required. The paste electrolyte of the present invention comprises a solvent with low to medium dielectric constant, exceeding those of pure linear carbonates (in the case of ethyl-methyl-carbonate (EMC), E _ 3) but being significantly less (E < 50) than those of pure cyclic carbonates (in the case of ethylene carbonate (PC), E - 65).
[231 JP H09-115505 discloses electrodes comprising a lithium transition metal in which powderous particles are coated with sintered clay. This technique is absolutely different from the present invention in view of kinds of application and materials.
[24] The present invention also provides a rechargeable lithium battery containing the paste electrolyte as defined above between anode and cathode.
[25] The paste electrolyte may be in a form of layer. A layer of the paste electrolyte (hereinafter, sometimes referred to as "paste electrolyte layer") can be located in any inner place of lithium battery so long as the paste electrolyte layer can separate anode and cathode to limit the anionic transport between the anode and cathode without sig-nificantly decreasing the lithium transport rate. Such separation may be achieved by one or more of the following:
[26] the paste electrolyte is embedded in the pores of the cathode;
[27] the paste electrolyte is applied as a thin layer between the cathode and separator, eventually penetrating the separator;
[28] the paste electrolyte is embedded in the pores of separator;
[29] the paste electrolyte is applied as a thin layer between the anode and separator, eventually penetrating the separator; and [30] the paste electrolyte is embedded in the pores of the anode.
[311 The layers of clay can be achieved by many different methods. In principle, it is possible to deposit (for example, by coating) a layer of paste-type electrolyte-swollen clay during an assembly of a battery cell. This method, however, is not easy to implement at the production level.
[32] In an embodiment according to the present invention, it is possible to deposit a layer of clay, swollen by a suitable solvent such as water, ethanol, NMP and the like, followed by drying. This method is especially suitable to coat a layer of clay onto the separators or onto electrodes. After assembly of a battery, electrolyte is injected and the dried layer slowly swells with electrolyte and forms the desired paste electrolyte layer.
[33] Another preferred method is to add the clay swollen by a suitable solvent to an electrode slurry before coating of the electrode slurry into electrodes. As an example, clay swollen by N-methyl-2-pyrrolidone (NMP) can be added to the NMP+PVDF-based electrode slurry containing the electrochemical active cathode or anode material.
Alternatively, the clay swollen by water can be added to a water-based slurry.
After coating and drying, the clay is located within the pores of the electrode, and after battery assembly and electrolyte injection, this clay is swollen by the electrolyte.
[34] The swelling of clay by a solvent such as water, ethanol and NMP may be supported by mechanical activation including, for example, but is not limited to ballmilling, beadniilling or kneading a mixture of clay and solvent.
[35] The other constitutional elements for rechargeable lithium batteries and the processes for preparation thereof are well known in the art to which the present invention pertains, thus the detailed description about them is omitted in the present disclosure.
Brief Description of the Drawings [36] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
[37] FIG. 1 is a graph showing the results of electrochemical test (cycle 1 and discharge rate performance) of the coin cells containing thick-electrode pellets in Example 5.
Mode for the Invention [38] Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for the purpose of illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention.
[39]
[40] [Example 1] Swelling of clay in electrolyte [41] A commercial synthetic clay ("optigel SH", SuedChemie, Germany) was used.
The clay was in the form of a coarse, free flowing powder. The clay was dried at 180C to lower the water content. 10 g of the dried clay was added to 20 g of electrolyte (1M
LiPF 6 in EC/EMC (1 : 2)). After several weeks of storage at room temperature in a sealed PP vial in a glovebox, a homogeneous white paste was achieved. No mechanical force like grinding, agitating etc. was applied. This experiment demonstrates that the used clay swells in an electrolyte with medium dielectric constant.
[42]
[43] [Example 2] Swelling of clay in NMP
[44] A mixture of 86% NMP and 14%(w/w) clay was ballmilled using a planetary mill.
A semi-transparent, homogeneous white paste was achieved.
[45]
[46] [Example 3] Addition of clay paste to electrode slurries [47] The clay-NMP paste of Example 2 was added to an NMP-based anode (MCMB) and an NMP-based cathode (Li-manganese-spinel) slurry, respectively, followed by homogenizing. The total content of clay per active materials in the slurry was 1%
(w/w). The compositions (active material: PVDF: carbon black) of the cathode and anode slurry were 94: 3 : 3 and 94.5 : 4.5 : 1, respectively.
[48] The slurries were coated on aluminum foil and copper foil, respectively, and then dried. An improved adhesion was observed, compared with electrodes coated from the slurry without clay.
[49]
[50] [Example 4] Storage properties of clay containing ion cells [51] Coin-full cells were prepared using the electrodes of Example 3. The total 4 types of cells were prepared as the following:
[52] (i) anode with clay - cathode with clay [53] (ii) anode with clay - cathode without clay [54] (iii) anode without clay - cathode with clay [55] (iv) anode without clay - cathode without clay.
[56] Storage properties of charged cells (65 C) and cycling stability (50 C) were in-vestigated. Cells containing clay in the anode showed clearly improved storage properties.
[57] 2 cells of each type were tested. First cells were tested for the purpose of measuring rate performance & capacity. The rate performance was similar for all cells.
Then cells were charged to 4.2 V and stored for 3 days at 65 C. After storage, cells were cycled at room temperature for 2 cycles (3.0 - 4.2 V) starting with discharge to 3.0 V.
While the first discharge capacity is the remaining capacity, the 2nd discharge capacity is the reversible capacity. After this test, another storage was performed at 65 C
for 10 days.
The results for the cell showing two with better results are summarized in below.
[58] <TABLE 1>
[59]
Before storage After storage 1 After storage 2 Cathode fully charged fully charged capacity for 3d 65"C for 10d 65''C
(mAh/g) remaining reversible remaining reversible Anode & cathode 91.6 70.0 77.0 49.2 56.7 with clay (100%) 76.4% 84.0% 53.7% 61.9%
Anode clay 93.0 72.8 78.1 49.4 56.6 Cathode no clay (100%) 78.2% 83.9% 53.1% 60.8%
Anode no clay 90.0 63.1 69.5 22.2 31.03 Cathode clay (100%) 70.1% 77.2% 24.6% 34.5%
Anode & cathode 90.8 66.6 72.1 40.2 47.0 without clay (100%) 73.4% 79.4% 44.2% 51.8%
[60] The above result shows that the addition of clay has a positive effect on the storage properties (remaining and reversible capacity) of Li-batteries.
[61]
[62] [Example 5] Change of electrolyte properties [63] It is difficult to exactly measure transport properties of electrolyte, i.e., conduction and transference number. Therefore, in this experiment, the ionic transport of electrolyte was indirectly measured by comparing the rate performance of cells with clay with those of cells without clay. In this connection, it is important to achieve a similar cell geometry such as thickness of electrodes, porosity, loading, etc., and it is also important that the electrolyte transport is the only rate-limiting step.
To achieve those requirements coin cells with pellet type electrodes were prepared.
[64] The active anode material was MCMB and the active cathode material was LiCoO2 . The cathode mass was 239 - 240.2 mg. The composition (LiCoO2 : PVDF : Carbon Black : Clay) was 85 : 7 : 8 for cathodes without clay and 85 : 6.07: 6.93: 2 and 85 : 4 : 4 :7 for cathodes with clay, respectively. The thickness of pellets was 0.48 - 0.51 mm and the diameter was 15 mm. The anode pellets were free of clay and had a composition (MCMB : PVDF : Carbon Black) of 90 : 7: 3. The anode mass was 149.9 150.4 mg. The thickness of the pellets was 0.49 - 0.52 mm. The diameter was 16 mm. Electrode pellets were prepared by drying an NMP-PVDF-based slurry, followed by grinding and controlled pressing of pellets. Clay-containing slurries were prepared by adding the clay-NMP paste of Example 2.
[65] Coin cells were assembled. After very slow formation (C/100, 1C=150 mA/g cathode) for 10h, the cells were charged to 4.25 V. The charging occurred by repeated sequences of C/20 charge for 2 h (or until 4.25 V cutoff was reached) and rest for 2 h. All electrochemical testing was performed at 25 C.
[66] Discharge was at C/20, C/10 and C/5 rate. The results of the best 3 cells out of 9 prepared cells are expressed in FIG 1. First, it is important to note that cells with a total thickness of 1mm are only limited by the electrolyte transport. All other processes such as electronic conduction, solid diffusion within single particles and the like are orders of magnitude slower. The cell with 7% clay clearly shows the largest electrolyte resistance, which can be seen by the gap between 1st charge and 1st discharge curve, as well as by the larger relaxation during the rest periods during the charge. We also see the larger electrolyte resistance of the 7% clay cell during discharge. The gap between C/20 and C/5 discharge curve is clearly larger for 7% clay compared with 0 or 2%
clay. Additionally the discharge capacity at a slow rate is less, and the reason for this is not clear. However, despite the larger electrolyte resistance and the lower capacity, the 7% clay cell shows a good C/5 discharge capacity. This result strongly illustrates that the Li transference number of the electrolyte in the 7% clay cell increases.
As a result, there is less electrolyte depletion, and the discharge profile bends more slowly down.
The results are summarized in TABLE 2 below.
[67] <TABLE 2>
[68]
Discharge capacity Discharge capacity Discharge capacity (C/20) mAh/g (C/1C) mAh/g (C/5) mAh/g Clay: 0% 144 (100%) 120 (83%) 91 (63%) Clay 2% 143(100%) 127 (89%) 97(68%) Clay 7% 131 (100%) 122 (93%) 96(73%) [69] As can be seen in TABLE 2, the discharge capacities associated with the discharge at C/20 clearly increase with the increasing content of clay.
Industrial Applicability [70] As apparent from the foregoing, the paste electrolyte according to the present invention can improve the electrochemical properties and cycling stability of rechargeable lithium batteries by limiting the anionic transport between anode and cathode without significantly decreasing the lithium transport rate, particularly during fast charge and discharge.
[71] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modi-fications, additions and substitutions are possible, without departing from the scope of the invention as disclosed in the accompanying claims.
Claims (15)
1. A paste electrolyte comprising an organic solvent of a dielectric constant (.epsilon.): 3 < .epsilon. < 50, soluble lithium salts, and clays, with the clays being swollen and exfoliated by the organic solvent, wherein the size of exfoliated clay sheets does not exceed 2 micrometers, wherein said solvent contains more than 50% by volume of one or more linear carbonates and less than 50% by volume of one or more cyclic carbonates or cyclic esters.
2. The paste electrolyte according to claim 1, wherein said solvent contains more than 60% by volume of one or more linear carbonates and less than 40% by volume of one or more cyclic carbonates or cyclic esters.
3. The paste electrolyte according to claim 1, wherein said soluble lithium salts are selected from the group consisting of LiPF6, LiBF4, Li[N(SO2CF2CF3)2], lithium Bis(oxalato)borate, and lithium Bis(trifluoromethanesulfonyl)imide.
4. The paste electrolyte according to claim 1, wherein said soluble lithium salts are contained in a concentration exceeding 0.5 mol / liter solvent.
5. The paste electrolyte according to claim 1, wherein said clays are selected from the group consisting of hectorite, montmorillonite and alpha-zirconium phosphate.
6. The paste electrolyte according to claim 1, wherein said clays contain lithium or sodium.
7. The paste electrolyte according to claim 6, wherein said clays are phyllosilicates containing sodium.
8. The paste electrolyte according to claim 1, wherein the volume fraction of the solvent and salt in said paste electrolyte is more than 75% but less than 99%.
9. The paste electrolyte according to claim 1, wherein the size of exfoliated clay sheets is significantly less than 0.5 micrometers.
10. A rechargeable lithium battery containing the paste electrolyte according to any one of claims 1 to 9 between anode and cathode.
11. The rechargeable lithium battery according to claim 10, wherein said paste electrolyte separates the anode and cathode by one or more of the following:
(a) the paste electrolyte is embedded in the pores of the cathode;
(b) the paste electrolyte is applied as a layer between the cathode and separator, eventually penetrating the separator;
(c) the paste electrolyte is embedded in the pores of the separator;
(d) the paste electrolyte is applied as a layer between the anode and separator, eventually penetrating the separator; and (e) the paste electrolyte is embedded in the pores of the anode.
(a) the paste electrolyte is embedded in the pores of the cathode;
(b) the paste electrolyte is applied as a layer between the cathode and separator, eventually penetrating the separator;
(c) the paste electrolyte is embedded in the pores of the separator;
(d) the paste electrolyte is applied as a layer between the anode and separator, eventually penetrating the separator; and (e) the paste electrolyte is embedded in the pores of the anode.
12. The rechargeable lithium battery according to claim 11, wherein said layer is prepared by coating a layer of clay swollen with a solvent onto an electrode surface or separator surface, followed by drying, and the final swelling of clay with electrolyte is achieved after the assembly of a cell and injection of electrolyte into the cell.
13. The rechargeable lithium battery according to claim 12, wherein said layer further comprises water, ethanol or N-methyl-2-pyrrolidone.
14. The rechargeable lithium battery according claim 12, wherein said clay is embedded into the pores of the anode or cathode by adding clay swollen by said solvent to an electrode slurry before coating.
15. The rechargeable lithium battery according claim 14, wherein said clay is swollen by N-methyl-2-pyrrolidone, and the swelling is supported by mechanical activation including ballmilling, beadmilling or kneading a mixture of clay and N-methyl-2-pyrrolidone.
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| JP5593982B2 (en) | 2010-09-03 | 2014-09-24 | 日産自動車株式会社 | Non-aqueous electrolyte composition and non-aqueous electrolyte secondary battery |
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| CN106058219B (en) * | 2016-08-11 | 2018-05-22 | 湖南瑞翔新材料股份有限公司 | Compound coating agent, high voltage cobalt acid lithium and preparation method thereof |
| WO2018237188A1 (en) | 2017-06-21 | 2018-12-27 | University Of Utah Research Foundation | Cathodes for use in lithium-air batteries |
| WO2019226674A1 (en) | 2018-05-21 | 2019-11-28 | University Of Utah Research Foundation | Composite solid electrolyte including lithium iron phosphate |
| CN109768321A (en) * | 2019-03-22 | 2019-05-17 | 广州大学 | A kind of lithium battery solid electrolyte and preparation method thereof based on the pillared clay of aluminium |
| CN109994722A (en) * | 2019-03-27 | 2019-07-09 | 华南理工大学 | A kind of Li1+xAlxTi2-x(PO3)4Cobalt acid lithium material of cladding and the preparation method and application thereof |
| CN110504487B (en) * | 2019-08-09 | 2020-06-16 | 电子科技大学 | Lithium ion battery electrolyte and preparation method thereof |
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| JPH08279354A (en) * | 1994-08-01 | 1996-10-22 | Ricoh Co Ltd | Electrode and secondary battery using the electrode |
| JPH08181324A (en) | 1994-12-27 | 1996-07-12 | Sharp Corp | Manufacture of semiconductor device |
| JPH09115505A (en) | 1995-10-16 | 1997-05-02 | Sanyo Electric Co Ltd | Lithium secondary battery and its manufacture |
| JPH1012269A (en) * | 1996-06-20 | 1998-01-16 | Sanyo Electric Co Ltd | Solid electrolyte and solid electrolyte battery |
| JPH1055718A (en) * | 1996-08-07 | 1998-02-24 | Polytec Design:Kk | Paste electrolyte |
| JP3635302B2 (en) * | 1997-02-17 | 2005-04-06 | 株式会社リコー | Secondary battery |
| JP3717092B2 (en) * | 1997-03-27 | 2005-11-16 | Ｔｄｋ株式会社 | Solid electrolyte, lithium secondary battery and electric double layer capacitor |
| US6544689B1 (en) * | 1999-06-30 | 2003-04-08 | North Carolina State University | Composite electrolytes based on smectite clays and high dielectric organic liquids and electrodes |
| US6821677B2 (en) * | 2001-03-29 | 2004-11-23 | Kabushiki Kaisha Toshiba | Negative electrode active material and nonaqueous electrolyte battery |
| US7077983B2 (en) | 2002-12-31 | 2006-07-18 | University Of Chicago | Polymer nanocomposites for lithium battery applications |
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| BRPI0621846B1 (en) | 2017-10-31 |
| CA2656401A1 (en) | 2008-01-17 |
| EP2038958A4 (en) | 2011-05-11 |
| EP2038958A1 (en) | 2009-03-25 |
| JP2009543316A (en) | 2009-12-03 |
| JP5372748B2 (en) | 2013-12-18 |
| WO2008007814A8 (en) | 2008-12-18 |
| EP2038958B1 (en) | 2017-09-06 |
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